Reduced cross-contamination between chambers in a semiconductor processing tool

ABSTRACT

In accordance with one aspect of the present invention, a method is provided for transporting a workpiece in a semiconductor processing apparatus comprising a transfer chamber, a process chamber, and a gate valve between the transfer chamber and the process chamber. The method comprises vacuum pumping the transfer chamber to achieve a first pressure in the transfer chamber and vacuum pumping the process chamber to achieve a second pressure in the process chamber. An inert gas is flowed into the transfer chamber and shut off in the process chamber. The transfer chamber is isolated from pumping, but pumping continues from the process chamber. The gate valve is opened after isolating the transfer chamber from pumping. The workpiece is then transferred between the transfer chamber and the process chamber. A definitive flow direction from transfer chamber to process chamber is thereby achieved, minimizing risk of back-diffusion.

REFERENCE TO RELATED APPLICATION

This application claims priority under 35 U.S.C. §119(e) to U.S.application No. 60/382,204, filed May 21, 2002.

FIELD OF THE INVENTION

The present invention relates to semiconductor processing tools and, inparticular, to methods of minimizing cross-contamination duringtransport of the wafers between chambers of such tools.

BACKGROUND OF THE INVENTION

Cluster tools used in the semiconductor processing of wafers or otherworkpieces typically comprise a central wafer handling chamber, ortransfer chamber, surrounded by a number of process chambers withinwhich various processes are carried out on the wafers (e.g., deposition,etching, doping, annealing and oxidizing). A robot is provided in thetransfer chamber for moving the wafers within the cluster tool. Thetransfer chamber is typically isolated from each of the process chambersby gate valves. The gate valves can be opened to allow the robot totransfer the wafers between the transfer chamber and the processchambers.

For reduced pressure processing, transfer of wafers between the transferchamber and the process chambers can be carried out at reduced pressure,thereby eliminating the need to pump down the process chamber after eachwafer transfer and increasing wafer throughput. It is important toprevent cross-contamination between the chambers during wafer transfer.Gaseous (homogeneous) cross-contamination takes place when gases fromone chamber are convectively or diffusively transported to anotherchamber, thereby contaminating the other chamber. For example, anoxidizing species used to grow a silicon dioxide or oxynitride film inone process chamber could contaminate another process chamber in whichan oxygen-free environment is desired, such as for epitaxial deposition.Additionally, particulate (heterogeneous) particulate can also ariseduring wafer transfer.

In the past, attempts have been made to control the flow of gasesbetween the chambers, and thereby reduce gaseous cross-contamination, bycreating a pressure differential between the transfer chamber and theprocess chamber to be accessed prior to opening the gate valvetherebetween. The intent is that, when the gate valve is opened, thegases will flow from the higher pressure chamber to the lower pressurechamber to prevent contamination of the higher pressure chamber. Variouspump systems have been devised for creating pressure differentialsbetween the chambers.

One problem with such systems is that creating a pressure differentialbetween the chambers does not necessarily ensure that the desired gasflow will occur upon opening of the gate valve. This is due in part tothe dependence of the pressure differential-induced flow on the absolutepressures in the chambers. In addition, a back flow or back diffusion ofthe gases into the (initially) higher pressure chamber can occur uponopening of the gate valve.

SUMMARY OF THE INVENTION

The present method ensures the occurrence of the desired flow betweenthe transfer chamber and the process chamber(s) upon opening of the gatevalve(s) between the chambers.

In accordance with one aspect of the present invention, a method isprovided for transporting a workpiece in a semiconductor processingapparatus comprising a transfer chamber, a process chamber, and a gatevalve between the transfer chamber and the process chamber. The methodcomprises operating a first pump connected to the transfer chamber toachieve a first pressure in the transfer chamber and operating a secondpump connected to the process chamber to achieve a second pressure inthe process chamber. An inert gas is flowed into the transfer chamber.The first pump is isolated from the transfer chamber. The gate valve isopened while the first pump is isolated from the transfer chamber andthe second pump continues to operate. The workpiece is then transferredbetween the transfer chamber and the process chamber.

In accordance with another aspect of the present invention, a method isprovided for transporting a workpiece in a semiconductor processingapparatus comprising a transfer chamber, a process chamber, and a gatevalve between the transfer chamber and the process chamber. The methodcomprises vacuum pumping to achieve a lower pressure in the processchamber than in the transfer chamber. An inert gas is flowed into thetransfer chamber. An inert gas is also flowed into the process chamber.The flow of inert gas into the process chamber is discontinued. The gatevalve is opened after discontinuing the flow of inert gas into theprocess chamber while continuing to flow inert gas into the transferchamber. The workpiece is then transferred between the transfer chamberand the process chamber.

In accordance with another aspect of the present invention, a method oftransporting a workpiece in a semiconductor processing apparatus isprovided. The method comprises pumping a first chamber of the processingapparatus to achieve a first pressure in the first chamber and pumping asecond chamber of the processing apparatus to achieve a second pressurein the second chamber. An inert gas is flowed into the first chamber. Agate valve located between the first chamber and the second chamber isopened. The pumping of the first chamber is discontinued prior toopening the gate valve and while the gate valve is opened. The workpieceis then transferred between the first chamber and the second chamber.

In accordance with another aspect of the present invention, a method isprovided for transporting a workpiece in a semiconductor processingapparatus comprising a transfer chamber, a process chamber, and a gatevalve between the transfer chamber and the process chamber. The methodcomprises vacuum pumping to achieve a lower pressure in the processchamber than in the transfer chamber. An inert gas is flowed into thetransfer chamber. An inert gas is also flowed into the process chamber.The gate valve is opened while continuing to operate the at least onepump. The flow of inert gas into the process chamber is kept off whilethe gate valve is opened. The workpiece is then transferred between thetransfer chamber and the process chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the invention will be readily apparent to theskilled artisan in view of the description below, the appended claims,and from the drawings, which are intended to illustrate and not to limitthe invention, and wherein:

FIG. 1 is a top plan view of a wafer processing apparatus in accordancewith a preferred embodiment of the present invention;

FIG. 2 is a simplified schematic view of the wafer processing apparatusof FIG. 1;

FIG. 3 is a chart illustrating the status of various components of theprocessing apparatus when the gate valve is opened or closed, inaccordance with the preferred embodiment of the invention; and

FIG. 4 is a flow chart illustrating a process of operating asemiconductor processing apparatus in accordance with a preferredembodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

While not separately illustrated in the figures, it will be understoodthat the process steps disclosed herein can be programmed into a processtool controller that is electrically connected to control gas flowvalves, mass flow controllers, gate valve actuators, substrate transferrobots, etc. The skilled artisan will readily appreciate that anapparatus can be provided with software programming or hard wiring toachieve the desired processing steps described herein.

With reference initially to FIG. 1, an exemplary semiconductorprocessing apparatus 20 is illustrated, comprising a central substrateor workpiece handling chamber, or referred to herein as a transferchamber 26, connected to at least one process chamber. FIG. 1 shows thehandling chamber 26 surrounded by a number of process chambers 30. Inthe illustrated embodiment, the semiconductor processing apparatus 20 isadapted for use in CMOS gate stack applications. The process chambers 30comprise a hydrogen fluoride (HF) vapor clean chamber 34, a siliconnitride chemical vapor deposition (CVD) chamber 36, and an atomic layerdeposition (ALD) chamber 38. It is to be understood, however, that thesemiconductor processing apparatus 20 illustrated in FIG. 1 is merelyexemplary. In alternative embodiments, the apparatus 20 can include agreater or lesser number of process chambers 30. For example, theapparatus 20 can include only one process chamber 30 connected to thetransfer chamber 26, or can include more than the illustrated threeprocess chambers 30. In addition, the apparatus 20 can be configured toperform additional or other types of processes, and can be configured tocarry out the same process in two or more of the process chambers 30.

The semiconductor processing apparatus 20 of the illustrated embodimenthas a modular design and meets Semiconductor Equipment and MaterialsInternational (SEMI) standardization requirements for convenientinterconnection between the transfer chamber 26 and the process chambers30. Each of the process chambers 30 is isolated from the transferchamber 26 by a gate valve 40 (see FIG. 2). The gate valves 40 can beopened to allow the transfer of a semiconductor wafer or other workpiecebetween the transfer chamber 26 and the process chambers 30 by aworkpiece handling robot 46 (see FIG. 2) located within the transferchamber 26.

In the illustrated embodiment, to minimize particle contaminants, thetransfer chamber 26 and process chambers 30 are preferably situatedwithin a gray room defined by a gray room wall 48. A first or transferchamber vacuum pump 50 is provided, either within the gray room or in aclean room on the opposite side of the gray room wall 48. In otherarrangements, no clean room or gray room is provided. In the illustratedembodiment, a second or process chamber vacuum pump 54 is provided foreach of the process chambers 30. The transfer chamber pump 50 andprocess chamber pumps 54 selectively communicate with the transferchamber 26 and the process chambers 30, respectively, via conductancelines 58 to regulate the pressures in the chambers 26, 30. Inalternative embodiments, however, a greater or lesser number of pumpscan be provided to service the transfer chamber 26 and the processchambers 30. For example, a single pump may service more than onechamber through various valved conductance lines, or more than one pumpmay comprise a pump “bank” for servicing a single chamber. Although notshown, it will be understood that each of the process chambers 30 isconnected to a source of purge gas and reactant gas(es) and that thetransfer chamber 26 is also connected to a source of purge gas 80 (seeFIG. 2). Thus, a gas distribution system includes purge gas inlets ineach of the process chambers 30 and in the transfer chamber 26.

With reference still to FIG. 1, a load lock chamber 62 is provided at afront end of the transfer chamber 26. The illustrated embodimentincludes two load lock chambers 62. Alternatively, however, a singleload lock chamber 62 or more than two load lock chambers 62 could beprovided. The load lock chambers 62 are isolated from the transferchamber 26 by gate valves (not shown). In the illustrated embodiment, aloading platform 68 is provided in front of the load lock chambers 62 toautomatically load wafers from cassettes (not shown), or load thecassettes themselves, into the load lock chambers 62. The loadingplatform 68 of the illustrated embodiment includes two shuttles 72, eachof which can accommodate up to two cassettes. Preferably, the cassettesare standard front-opening unified pod (“FOUPs”), which provide closedenvironments for the wafers. The cassettes can be empty to receivewafers, or can contain from one to twenty-five wafers to be processed.

To operate the wafer processing apparatus 20, a user enters a processrecipe into a controller (not shown). The process recipe may includeinstructions regarding process sequences, process times, processtemperatures, pressures and gas flows. In an exemplary process, one ofthe shuttles 72 positions a cassette in front of one of the load lockchambers 62. The load lock chamber 62 is then back-filled to atmosphericpressure. The load lock chamber 62 is opened, and a cluster platformrobot (not shown) transfers the wafers from the cassette or transfersthe cassette itself from the shuttle 72 to the load lock chamber 62. Theload lock chamber 62 is then closed and evacuated.

The gate valve between the active load lock chamber 62 and the transferchamber 26 is opened to allow the workpiece handling robot within thetransfer chamber 26 to access the cassette. The workpiece handling robotextends into the load lock chamber 62 and removes a workpiece (e.g.,wafer) from the load lock chamber 62. The gate valve is then closed, andthe robot moves the wafer towards the process chamber 30 to be accessed.

With reference now to FIG. 2, prior to opening the gate valve 40 betweenthe transfer chamber 26 and one of the process chambers 30, the transferchamber pump 50 and the pump 54 of the process chamber 30 to be accessedare operated, as necessary, to achieve a slightly lower pressure in theprocess chamber 30 than in the transfer chamber 26. Preferably, thepressure in the process chamber 30 prior to opening the gate valve 40 isslightly below its operating value during processing. In this manner theprocess chamber 30 is backfilled to process pressure during wafertransfer, as will be understood in view of the disclosure below. Theskilled artisan will appreciate, however, that the lower pressure in theprocess chamber 30 compared to the transfer chamber 26 can be providedin any desired manner. The pressure differential between the processchamber 30 and the transfer chamber 26 is preferably low enough to avoidgenerating a significant pressure wave upon opening of the gate valve40, which could stir particle contaminants in the processing apparatus20. The optimum pressure differential will depend upon a number ofdifferent factors, including the particular design of the apparatus 20.Preferably, the pressure differential is between about 100 mTorr and 5Torr. In a typical reduced-pressure workpiece transfer, however, apressure differential between the process chamber 30 and the transferchamber 26 of about 100 mTorr to 300 mTorr has been shown to beadvantageous. More preferably, the pressure differential between theprocess chamber 30 and the transfer chamber 26 is about 100 mTorr to 150mTorr. Thus, for example, if the pressure in the process chamber 30prior to opening the gate valve 40 is about 200 mTorr, the pressure inthe transfer chamber 26 is preferably between about 300 mTorr and 500mTorr, and more preferably between about 300 mTorr and 350 mTorr. Inanother arrangement, the process chamber 30 is pumped to about 1 Torrprior to opening the gate valve 40, the pressure in the transfer chamber26 is preferably about 3 Torr, such that the pressure differential isabout 2 Torr.

When the desired pressures are obtained in the transfer chamber 26 andthe process chamber 30 to be accessed, an inert or non-reactive gas(also known as purge or sweep gas), such as nitrogen (N₂), is flowedinto the transfer chamber 26 from a gas source 80 via a gas line 84.Alternatively, the inert gas may already be flowing into the transferchamber 26 during pumping of the transfer chamber 26 and the processchamber 30 to reach the desired pressures in the chambers 26, 30, inwhich case the flow of inert gas into the transfer chamber 26 may becontinued. Inert gas is often flowed in semiconductor process reactorsto exclude oxygen, moisture and particulates. The gate valve 40 betweenthe transfer chamber 26 and the process chamber 30 is then opened, whilethe pump 54 of the process chamber 30 continues to operate. Preferably,the inert gas flow is initiated in the transfer chamber 26 at least 2seconds, and more preferably at least 10 seconds prior to opening thegate valve 40 to the process chamber, and most preferably inert gas flowin the transfer chamber 26 continues while the gate valve is opened.

As the gate valve 40 is opened, the transfer chamber pump 50 preferablyis isolated from the transfer chamber 26. The pump 50 can be isolatedsimultaneously with opening. More preferably, the gate valve 40 isopened at least 1 second after isolating the transfer chamber pump 50from the transfer chamber 26, and most preferably the gate valve 40 isopened between about 2 seconds and 5 seconds after isolating thetransfer chamber pump 50. The isolation of the transfer chamber pump 50may be accomplished, for example, by closing a valve 88 in theconductance line 58 between the transfer chamber 26 and the transferchamber pump 50, by turning off the pump 50, reducing the pump 50 speed,on diverting the suction to another path.

Preferably, no inert gas is flowing within the process chamber 30 uponthe opening of the gate valve 40 between the transfer chamber 26 and theprocess chamber 30. The process chamber 30 is typically purged ofreactant and by-product gases with inert gas after processing in thechamber 30 is stopped. Thus, if the inert gas is flowing into theprocess chamber 30, it should be affirmatively discontinued as the gatevalve 40 is opened. Preferably, the gate valve 40 is opened afterdiscontinuing the flow of inert gas into the process chamber 30. Morepreferably, the gate valve 40 is opened at least 1 second afterdiscontinuing the flow of inert gas into the process chamber 30, andmost preferably the gate valve 40 is opened between about 2 seconds and10 seconds after discontinuing the purge flow within the process chamber30. It will be understood that, while no inert gas is directly providedto the process chamber 30 by way of an inert gas inlet opening to theprocess chamber 30 when the gate valve 40 is opened, inert gas isindirectly provided to the chamber by way of flow from the transferchamber 26 when the gate valve 40 is opened, as explained in more detailin the paragraph below.

In accordance with the preferred embodiments, a definable convectiveflow of inert gas from the transfer chamber 26 to the process chamber 30is generated upon the opening of the gate valve 40 between the chambers26, 30. The robot 46 then transports the wafer into the process chamber30, and the gate valve 40 is closed. Rather than merely creating apressure differential, the purge and pump state shown in FIG. 3 createsa definable flow of inert gas from the transfer chamber 26 to theprocess chamber 30 upon opening of the gate valve 40. Thus, thepotential for contamination of the transfer chamber 26 by contaminantsin the process chamber 30 is minimized. The velocity of the gas flowbetween the chambers 26, 30 can be adjusted, as desired, by operating amass flow controller located in the gas line 84 between the transferchamber 26 and the inert gas source 80.

In a particularly preferred embodiment, an inert gas curtain isgenerated at the transfer chamber side of the gate valve 40 between thetransfer chamber 26 and each of the process chambers 30. The inert gascurtain preferably is generated by gas jets (not shown) directed towardsthe process chamber 30 along the perimeter wall of the gate valve 40,thereby reducing the boundary layer thickness of the inert gas at theperimeter wall. As a result, back flow of the inert gas into thetransfer chamber 26 (along with any contaminants from the processchamber 30) is reduced. The amount of the inert gas flowed from thetransfer chamber 26 to the process chamber 30 can also generally bereduced without adversely affecting contamination.

When the processing of the wafer in the process chamber 30 has beencompleted, the method described above is repeated prior to opening thegate valve 40 to remove the wafer from the process chamber 30. Thus, thetransfer chamber pump 50 and the pump 54 of the process chamber 30 to beaccessed are again operated, as necessary, to achieve a slightly lowerpressure in the process chamber 30 than in the transfer chamber 26. Inone embodiment, the pressure in the process chamber is activelycontrolled to be at a lower level than in the transfer chamber prior toopening the gate valve. Accordingly, inert gas flows directly into thetransfer chamber 26 but flows only indirectly, through the gate valve40, into the process chamber 30. When the desired pressures are obtainedin the transfer chamber 26 and the process chamber 30 to be accessed,the inert gas is flowed or continued in the transfer chamber 26. Thegate valve 40 between the transfer chamber 26 and the process chamber 30is then opened, while the pump 54 of the process chamber 30 continues tooperate. Preferably, at the time the gate valve 40 is opened, thetransfer chamber pump 50 is isolated from the transfer chamber 26, andno inert gas flows into the process chamber 30. The pump 54 of theprocess chamber 30, however, continues to operate, and the inert gascontinues to flow into the transfer chamber 26. The robot 46 transportsthe wafer out of the process chamber 30, and the gate valve 40 isclosed. The wafer can then be transferred, as desired, to anotherprocess chamber 30, to a cooling station (not shown), or back to thecassette.

The method described herein may be carried out each time one of the gatevalves 40 between the transfer chamber 26 and one of the processchambers 30 is opened. By creating a definable flow of inert gas fromthe transfer chamber 26 to the process chamber 30 upon opening of thegate valves 40 between the transfer chamber 26 and each of the processchambers 30, back flow and back diffusion of contaminants from theprocess chambers 30 to the transfer chamber 26 are minimized. As aresult, the reactants or reaction products present in one processchamber 30 are prevented from entering the transfer chamber 26, fromwhich they might subsequently contaminate other process chambers 30 orotherwise undesirably react with materials in the transfer chamber 26,causing, e.g., corrosion.

FIGS. 3 and 4 summarize the pump and purge status of the transfer andprocess chambers, relative to the gate valve opening and closing,according to the preferred embodiment of the present invention. Asillustrated in FIG. 4, while the gate valve is closed (and typicallyprocessing is being conducted inside the process chamber) conditions areestablished 100 such that a lower pressure is present in the processchamber as compared to the transfer chamber. This ensures an initialflux of gases in the direction of the process chamber upon opening ofthe gate valve. When a transfer of substrates or workpieces is desired,the controls are programmed to first turn OFF 110 the transfer chamberpump and the process chamber purge. As indicated in FIG. 3, preferablythe transfer chamber purge and the process chamber pump are maintainedin their ON conditions. Preferably, enough time passes to allow thesystem to stabilize to avoid turbulent flow upon opening the gate valve.The gate valve is then opened 120. Because purge gas flow continues toflow in the transfer chamber, without any pumping action, and becausepurge gas has been turned OFF to the process chamber while the vacuumpump continues to pull gases through the process chamber, the purge gashas a definitive flow direction from the transfer chamber to the processchamber. This definitive flow direction minimizes risk of back diffusionof homogeneous or heterogeneous contaminants or residual reactants fromthe process chamber out to the transfer chamber.

Workpieces can then be transferred 130 between the process chamber andthe transfer chamber. For example, a processed wafer can be removed fromthe process chamber, and a fresh wafer can be exchanged and placedinside the process chamber. Preferably, the fresh wafer is alreadypresent in the transfer chamber for this exchange, such that other gatevalves do not need to be opened. For example, the transfer chamber caninclude a staging area for the fresh wafer and a cooling station for theprocessed wafer. In other arrangements, multiple robots, multiple endeffectors, or multiple spots can be provided on a single robot toobviate the need for stations. In still other arrangements, a buffer orload lock is provided for wafers for performing exchange.

It should be noted that certain objects and advantages of the inventionhave been described above for the purpose of describing the inventionand the advantages achieved over the prior art. Of course, it is to beunderstood that not necessarily all such objects or advantages may beachieved in accordance with any particular embodiment of the invention.Thus, for example, those skilled in the art will recognize that theinvention may be embodied or carried out in a manner that achieves oroptimizes one advantage or group of advantages as taught herein withoutnecessarily achieving other objects or advantages as may be taught orsuggested herein.

Moreover, although this invention has been disclosed in the context ofcertain preferred embodiments and examples, it will be understood bythose skilled in the art that the present invention extends beyond thespecifically disclosed embodiments to other alternative embodimentsand/or uses of the invention and obvious modifications and equivalentsthereof. For example, in alternative embodiments, the processingapparatus 20 might have only one or any other suitable number of processchambers 30 connected to the transfer chamber 26. It is furthercontemplated that various combinations and subcombinations of thespecific features and aspects of the embodiments may be made and stillfall within the scope of the invention. For example, in some instances,it may be desirable to isolate the transfer chamber pump 50 prior toopening the gate valve 40 between the chambers 26, 30 and notdiscontinue the flow of inert gas to the process chamber 30. In otherinstances, for example, it may be desirable to discontinue the flow ofinert gas to the process chamber 30 prior to opening the gate valve 40between the chambers 26, 30 and not isolate the transfer chamber pump50. Accordingly, it is intended that the scope of the present inventionherein disclosed should not be limited by the particular disclosedembodiments described above, but should be determined only by a fairreading of the claims that follow.

We claim:
 1. A method of transporting a workpiece in a semiconductorprocessing apparatus comprising a transfer chamber, a process chamber,and a gate valve between the transfer chamber and the process chamber,the method comprising: operating a first pump connected to the transferchamber to achieve a first pressure in the transfer chamber; operating asecond pump connected to the process chamber to achieve a secondpressure in the process chamber; flowing an inert gas into the transferchamber; isolating the first pump from the transfer chamber; opening thegate valve while the first pump is isolated from the transfer chamberand the second pump continues to operate; and transferring the workpiecebetween the transfer chamber and the process chamber through the openedgate valve.
 2. The method of claim 1, wherein the second pressure isless than the first pressure.
 3. The method of claim 1, wherein no inertgas flows directly into the process chamber at the time of opening ofthe gate valve.
 4. The method of claim 1, wherein the gate valve isopened between about 2 seconds and 5 seconds after the isolating of thefirst pump.
 5. The method of claim 1, wherein the isolating of the firstpump comprises closing a valve in a gas line connecting the first pumpto the transfer chamber.
 6. The method of claim 1, wherein the isolatingof the first pump comprises shutting off the first pump simultaneouslyor after opening the gate valve.
 7. A method of transporting a workpiecein a semiconductor processing apparatus comprising a transfer chamber, aprocess chamber, and a gate valve between the transfer chamber and theprocess chamber, the method comprising: vacuum pumping to achieve alower pressure in the process chamber than in the transfer chamber;flowing an inert gas into the transfer chamber; flowing an inert gasinto the process chamber; discontinuing the flow of inert gas into theprocess chamber; opening the gate valve after discontinuing the flow ofinert gas into the process chamber while continuing to flow inert gasinto the transfer chamber; and transferring the workpiece between thetransfer chamber and the process chamber.
 8. The method of claim 7,wherein the gate valve is opened between about 2 seconds and 10 secondsafter discontinuing the flow of inert gas into the process chamber. 9.The method of claim 7, wherein the inert gas flow is initiated in thetransfer chamber at least 10 seconds prior to opening the gate valve.10. The method of claim 7, further comprising continuing to vacuum pumpthe process chamber while the gate valve is open.
 11. The method ofclaim 10, further comprising isolating the transfer chamber from vacuumpumping while the gate valve is open.
 12. The method of claim 7, furthercomprising generating an inert gas curtain at a side of the gate valveadjacent the transfer chamber.
 13. The method of claim 12, wherein theinert gas curtain is generated by inert gas jets directed towards theprocess chamber along a perimeter wall of the gate valve.
 14. A methodof transporting a workpiece in a semiconductor processing apparatus,comprising: pumping a first chamber of the processing apparatus toachieve a first pressure in the first chamber; pumping a second chamberof the processing apparatus to achieve a second pressure in the secondchamber; flowing an inert gas into the first chamber; opening a gatevalve located between the first chamber and the second chamber;discontinuing pumping the first chamber prior to opening the gate valveand while the gate valve is open; and transferring the workpiece betweenthe first chamber and the second chamber.
 15. The method of claim 14,wherein the first pressure is greater than the second pressure.
 16. Themethod of claim 15, wherein the second pressure is below the operatingpressure in the second chamber during processing of the workpiece. 17.The method of claim 14, wherein no inert gas is flowing into the secondchamber immediately prior to opening the gate valve.
 18. The method ofclaim 17, further comprising generating an inert gas curtain at a sideof the gate valve adjacent the first chamber.
 19. The method of claim18, wherein the inert gas curtain is generated by inert gas jetsdirected towards the second chamber along a perimeter wall of the gatevalve.
 20. The method of claim 14, wherein the first chamber is atransfer chamber.
 21. A method of transporting a workpiece in asemiconductor processing apparatus comprising a transfer chamber, aprocess chamber, and a gate valve between the transfer chamber and theprocess chamber: vacuum pumping to achieve a lower pressure in theprocess chamber than in the transfer chamber; flowing an inert gas intothe transfer chamber; flowing an inert gas into the process chamber;opening the gate valve while continuing to pump the process chamber;keeping the flow of inert gas into the process chamber off while thegate valve is opened; and transferring the workpiece between thetransfer chamber and the process chamber through the opened gate valve.22. The method of claim 21, wherein the processing apparatus comprisesat least two process chambers connected to the transfer chamber.
 23. Themethod of claim 21, wherein the pressure in the process chamberimmediately prior to the opening of the gate valve is between about 100mTorr and 5 Torr less than the pressure in the transfer chamber.
 24. Themethod of claim 21, wherein the pressure in the process chamberimmediately prior to the opening of the gate valve is between about 100mTorr and 300 mTorr less than the pressure in the transfer chamber. 25.The method of claim 21, wherein keeping the flow of inert gas into theprocess chamber off comprises discontinuing the flow of inert gas intothe process chamber at least 1 second prior to opening the gate valve.